Concrete walls and other concrete structures, are typically made by building a form. Unhardened concrete is poured into the form space provided by the form. Once the concrete hardens, the form walls can be removed. In some cases the form walls can remain in place after the structure has been made, and can for example serve an additional purpose such as providing insulation.
It is known to make the form walls from a series of interconnected panels. It is also known to use foamed plastic materials, including foamed polystyrene, for such panels.
Typically, the panels are held in place to provide the form when the concrete is poured in the form space, by providing tie-rods that stretch between two spaced panels. Typically the rods pass from an inner surface of the panels and join with some kind of end connector.
With reference to United States patent application publication no. 2002/0092253 published Jul. 18, 2002, a method is described whereby an anchor member is embedded in a foam panel. During the formation of the foam panel, the panel is injection formed so as to surround the anchor member. This may create a relatively strong connection between the panel and the anchor member. Despite the obvious advantages of such a connection, manufacturing of such plastic panels requires special molding equipment, which allows panels to be formed with installed anchor members. Such equipment and associated methods are expensive and don't allow the use of a common foam panel produced by industry for wall and roof thermal insulation. In some foamed panel applications for formwork, it is not desirable that the anchor member be fixed relative into the panel during the forming process. In particular, in some applications, it is desirable that the anchor member or connector be free to rotate relative to the panel so it can be secured firmly to an end of a tie-rod.
The building of forms using such foam plastic panels is assisted by the availability of numerous apertures in order to receive corresponding tie-rods and/or connectors.
It should be noted that known methods of forming apertures, such as milling, are not effective for forming apertures in foam plastic due to its low strength. Additionally, apertures formed with mechanical impacting on foam plastic, is very complicated to control because of the coarse structure of foam plastic.
U.S. PTO application Ser. No. 10/253,843 filed on Sep. 24, 2002 by the same applicant, the contents of which, are hereby incorporated by reference, discloses a method and a design for apparatus for forming apertures in foamed plastic panels. The method and apparatus include a carriage mounted on tracks to travel on the frame. The carriage is adapted to hold the panels and there is a mechanism mounted above the panel to move the aperture forming instruments towards the panel. The aperture forming instruments consist of a longitudinal tubular probe heated by an electrical resistance coil with no contact with the panel and cause apertures to be formed there through. The coil is heated by electrical current, using transformers.
However, this apparatus has a relatively low production output if a large number of apertures are required for the panel that will be used in the form. The design of the instrument results in a relatively unheated (“cold”) end. To heat the end portion of the instrument to generate a suitably hot thermal field under the instrument's end, the amount of beating of the main body of the instrument must be significantly increased. However, in heating the end for non-contact entering into a panel made of a foamed plastic material, the heat in the body is so high that it is difficult to form commensurable apertures with a diameter just a small amount larger than the diameter of the instrument. Additionally, this instrument doesn't allow forming the aperture with a complicated shape. Also, because the instrument is moving toward and through the panel, it becomes colder under the airflow movement and this causes a disruption to the thermal field around the heating instrument. This results in a decrease in temperature of the thermal field, which leads to a need to increase the consumed electrical power volume, to provide a given temperature and thermal field. In addition, use of the transformers as the electricity source for coils increases the cost of such a machine.
Accordingly, it is desirable to provide an improved method and apparatus for efficiently providing a plurality of apertures in foam plastic panels, particularly of the type that are used for construction.